Singapore researchers convert sewage sludge into hydrogen and animal feed

Singaporean scientists have developed a method of converting sewage sludge into hydrogen and animal feed.

Researchers at the Nanyang Technological University (NTU), Singapore, created a three-step process powered by solar electricity using mechanical, chemical and biological techniques to challenge conventional technologies like anaerobic digestion (AD).

Sewage sludge is a semi-solid by-product of wastewater treatment, consisting of organic and inorganic materials, microorganisms, heavy metals and other contaminants.

The NTU process begins by breaking down the sewage sludge. A chemical treatment then separates heavy metals from organic materials.

Using a solar-powered electrochemical process, the researchers use electrodes to transform the organic materials into products like acetic acid – which is used for food production – and hydrogen gas.

Finally, light-activated bacteria are introduced into the processed liquid stream, which converts nutrients into single-cell protein which can be used for animal feed.

Prof. Li Hong from NTU’s School of Mechanical and Aerospace Engineering (MAE), said the method could help reduce environmental damage from sludge while creating renewable energy and sustainable food.

According to the team’s lab results, the process achieves around 10% energy efficiency, producing up to “13 litres of hydrogen per hour” – equivalent to around 0.028kg of hydrogen, highlighting the early-stage nature of the research.

It also converted 63% of the sludge’s organic carbon into single-cell protein – compared to the typical 50% conversion from an AD.

While the development is hoped to showcase the viability of managing waste, the team acknowledged more studies are needed to determine whether it could be scaled up.

“A key challenge is the cost of using an electrochemical process to completely break down organic materials and extract all heavy metals from waste,” NTU said. “Additionally, designing a complex system for a wastewater treatment facility adds to the difficulty.”